Stability analysis for propped walls

Factors of Safety are presented in a table of the following form:-

FoS for toe Toe elev. for Strut force elev. = -2.00 FoS = 2.000 for F=1.000 --------------- ------------- ----------- Stage --- G.L. --- Strut Factor Moment Toe Wall Strut No. Act. Pass. Elev. of equilib. elev. Penetr force Safety at elev. -ation kN/m run 3 11.00 6.00 10.00 3.104 n/a 1.30 4.70 90.12 Case A Case B Case C

Heading InterpretationG.L. Act. Ground level, active side, at this stage.

G.L. Pass. Ground level, passive side, at this stage.

Strut Elev. Strut or anchor elevation.

FoS for toeCase Aelev. = xxxx Calculated Factor of Safety for the toe elevation given in the data under "Wall

Properties". If the FoS is not adequate at any stage, the wall should be made deeper.

Moment equilib. Not applicable to propped walls.at elev.

Toe elev. for Case BFos = yyyyy Toe elevation required to achieve the Factor of Safety given in the data under

"Analysis Options".

Wall penetration Wall penetration below GL on the passive side penetration (corresponding to the above toe elevation).

Strut force Case Cfor F = zzzzz The strut force corresponding to an assumed Factor of Safety (usually 1) as

given under "Analysis Options".

For single propped walls the program does three calculations:-A) Factor of safety for the given wall depth.B) Prop force for a given factor of safety, Ft, specified by the user (usually 1).C) Required wall depth for a given factor of safety, Fp, specified by the user. If the wall is not deep

enough to provide the specified factor of safety Fp, a message is printed.

The program may print the message:-

Conditions not suitable for factor of safety calculation

This may be because:-a) The strut force is negative i.e. the resultant of the active pressures acts at a lower elevation than

the resultant of the passive pressures!b) There is no nett overturning moment; the active pressures are small or zero, possibly due to the

presence of cohesive soil.c) The wall is trying to fail from right ("passive") to left ("active"). If you want to calculate the factor

of safety under these conditions you would have to reverse the data.